4. Rich Internet applications. A grab bag of technologies, including AJAX and Flash, enabled Web apps to replace client-server applications across the enterprise. As long as programmers avoided browser-specific features, new application versions no longer needed client upgrades -- which, among other things, allowed software as a service to bloom. The shift to Web apps also democratized programming, fostering lightweight development using scripting languages.
5. Storage area networking. Pooled, block-addressable storage spread across multiple storage arrays connected via FibreChannel was a novel idea at the outset of this decade. SANs offered fast access to big storage, improved reliability and availability, and awesome scalability. Separating enterprise data and putting it on its own reliable high-speed network also made server failures far less critical.
Sorry, did I leave out the iPhone? Well, it's not an enterprise technology -- yet. But there are many viable alternatives to choose from in building your own list. Take blade servers, for one. Or VoIP. Or network attached storage. Or ... Windows XP?
If the '80s was the decade of the PC, and the '90s was the decade of the Internet, then the one thing the '00s lacked was a big, single, defining technology. Though you can't call it a technological advance, I think of the '00s as the decade of data. Thanks in part to Enron, we compulsively saved petabytes of the stuff. And there it sits, while at the same time, we have tons of cheap surplus computing power -- spreading from underutilitzed CPUs in the datacenter to server farms in the cloud. With luck, the teens will be the decade in which we finally figure out how to put the two together on an unprecedented scale.